JPH0563172A - Semiconductor device and its manufacture - Google Patents

Abstract

PURPOSE:To form high-sensitivity photodetectors and high-speed scannable drive elements over the same substrate of the same constitution by photodetectors having amorphous semiconductor layers and thin film transistors having polycrystalline semiconductor layers. CONSTITUTION:A glass substrate 10 is spread with an Al film 9 of about 120nm thickness, which is then spread with a low-hydrogenated SiN film 4 of about 350nm. Further, the part of a photodetector 1 is spread with a low-hydrogenated non-doped amorphous silicon film 11, and the part of a TFT 2 with a low- hydrogenated polycrystalline silicon (poly-Si) film 5. The poly-Si film 5 has an a-Si film 11 at a part, which is spread with a phosphin-doped amorphous silicon film 6 and a Cr/Al double layer film 7. This design enables a photodetector having an amorphous semiconductor layer and a thin film transistor having a polycrystalline semiconductor layer as the active layer to be formed on the same substrate from the same film constitution, thereby manufacturing a semiconductor device having high-sensitivity photodetectors and high-speed scannable thin film transistors with a high manufacture efficiency.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device having a thin film and a manufacturing method thereof, and more particularly to a thin film device such as a display and an image sensor using an amorphous semiconductor.

[0002]

2. Description of the Related Art Conventionally, in an apparatus having a thin film as a constituent element, when an electronic component is required as a driving unit, L
The electronic circuit part was formed by mounting SI on a thin film substrate. In recent years, with the progress of thin film technology, it has become possible to directly form electronic circuit functions such as a thin film transistor (TFT) and a diode on a thin film substrate. For example, in a liquid crystal display, the liquid crystal is conventionally driven by a simple matrix circuit, but in recent years, the contrast is improved by switching with an amorphous silicon thin film transistor (a-Si TFT) formed for each pixel of the liquid crystal. It is possible. As a result, the image quality of the liquid crystal display is
It is possible to improve to RT level. Further, in a contact type image sensor used for image input of a facsimile or a scanner, a switch provided for each light receiving element is formed by a TFT on the same substrate as the light receiving element, so that the number of separately mounted LSIs can be reduced. Can be reduced. This can significantly reduce costs, and
400d
It is possible to easily handle high-definition reading of pi.

In the contact type image sensor, hydrogenated amorphous silicon (a-S) having high photosensitivity in the visible light wavelength region is used for the photodiode and the photoconductor of the light receiving element.
i: H) and cadmium sulfide (CdS) are used.
On the other hand, as an element for a drive circuit of a light receiving element, L of crystalline silicon, which has high mobility and can realize a high-speed scanning circuit.
Polysilicon (poly-Si) TFTs that can be formed by SI or a thin film process are suitable.

When the light receiving element and the driving circuit element are formed on the same substrate, if CdS is used for the light receiving element, it is necessary to form the driving circuit element and silicon by a different process. On the other hand, when a-Si: H is used for the light receiving element, it is possible to simultaneously form the silicon films of the light receiving element and the drive circuit element in the same process.
There is a great merit that the number of manufacturing processes can be reduced.

However, it is necessary to use amorphous silicon (a-Si: H) containing hydrogen for the highly sensitive light receiving element, and crystalline silicon is used for the driving circuit element capable of high-speed scanning. There is a need. For example, when a driving circuit element is formed of an a-Si: H film in accordance with the light receiving element, the mobility of the driving circuit element is 0.2 to 0.6 cm.
It becomes as small as ² / Vs. Therefore, when the light-receiving element and the driving circuit element are made of the same silicon film at the same time, it is difficult to realize a contact-type image sensor with high sensitivity and high-speed scanning.

Therefore, IEEE. Electron Devices Vol. ED-
32, No. 8, p1546, 1985, in a contact type image sensor in which a light receiving element and a driving circuit are formed on the same substrate, first, a light receiving element made of an a-Si film is formed, and then, A method of forming a thin film transistor (poly-Si TFT) made of a polycrystalline silicon film as a driving circuit in another process has been announced. In addition, Japanese Patent Laid-Open No. 2-1
In the TFT described in 30912, first, an a-Si film is formed on a glass substrate at a low temperature, and the upper portion thereof is crystallized by a laser anneal, so that a poly-S film having a high operating speed is obtained.
A method of forming an iTFT on an inexpensive glass substrate having a low melting point has been proposed. Furthermore, JP-A-2-14355
In the contact type image sensor described in 9, in which the light receiving element and the driving circuit are formed on the same substrate, a desired region of the amorphous silicon layer is laser-annealed to form a poly-Si layer, and this portion is formed. A method of making an active layer of a thin film transistor has been proposed.

[0007]

However, the method of forming the drive circuit in another process after forming the light receiving element has a problem that the process is complicated and long, and the manufacturing efficiency is deteriorated. Further, the method of converting the a-Si layer into poly-Si by laser annealing to form the active layer of the thin film transistor is a-S formed by a usual method.
When the i layer is used, there is a problem in that the film deteriorates due to the laser light, film peeling occurs, and the performance of the thin film transistor deteriorates.

An object of the present invention is to provide a semiconductor device in which a highly sensitive light receiving element and a driving element capable of high speed scanning can be formed on the same substrate with the same film structure, and a manufacturing method thereof. It is in.

[0009]

According to the present invention, there is provided a semiconductor device having a light receiving element having an amorphous semiconductor layer for photoelectric conversion and a thin film transistor having a polycrystalline semiconductor layer. ..

The light receiving element may further include a polycrystalline semiconductor layer, and the thin film transistor may further include an amorphous semiconductor layer.

Further, the polycrystalline semiconductor layer of the thin film transistor may partially include an amorphous semiconductor layer. The polycrystalline semiconductor layer of the thin film transistor may have a relatively low hydrogen concentration as compared with other semiconductor layers of the thin film transistor.

According to another aspect of the present invention, a high-reflectance portion having a reflectance higher than that of the amorphous semiconductor is formed on the amorphous semiconductor layer, and the high-reflectance portion is irradiated with laser light. A method for manufacturing a semiconductor device is provided, which comprises selectively crystallizing a semiconductor thin layer in which the high reflection portion is not formed by uniformly irradiating the amorphous semiconductor.

[0013]

The light receiving element having the semiconductor layer for performing photoelectric conversion and the thin film transistor having the semiconductor layer for processing the output signal of the light receiving element are formed on the substrate. The semiconductor layer of the light receiving element has an amorphous semiconductor layer, and by using this layer as a layer for performing photoelectric conversion, the light receiving element can have high sensitivity, and the semiconductor layer of the thin film transistor is a polycrystalline semiconductor layer. By using this layer as an active layer of the thin film transistor, the thin film transistor can be scanned at high speed.

Further, the light receiving element and the thin film transistor have a semiconductor layer having two layers of a polycrystalline semiconductor layer and an amorphous semiconductor layer, so that the light receiving element and the thin film transistor have the same film structure and are formed on the same substrate. It becomes possible to do. By adopting this film structure, the light receiving element and the thin film transistor can be formed in the same step, and the manufacturing efficiency can be improved. In the light receiving element, the amorphous semiconductor layer of the two semiconductor layers of polycrystalline and amorphous is used as the photoelectric conversion layer, and the polycrystalline semiconductor layer is not used as the photoelectric conversion layer. A thin film transistor uses a polycrystalline semiconductor layer as an active layer and does not use an amorphous semiconductor layer as an active layer among two semiconductor layers of polycrystalline and amorphous.

Further, an amorphous semiconductor layer is provided in the same film on the light receiving element and the thin film transistor, the light receiving element uses this amorphous semiconductor layer as a photoelectric conversion layer, and the thin film transistor heats this amorphous semiconductor layer. The polycrystalline semiconductor layer thus obtained can be used as an active layer. Also in this structure, the light receiving element and the thin film transistor can be formed on the same substrate in the same step, and only the step of heating the amorphous semiconductor layer in the thin film transistor portion to form the polycrystalline semiconductor layer is added. When the amorphous semiconductor layer that is polycrystallized by heating is a layer having a low hydrogen content, it is less susceptible to damage such as film peeling and surface roughness due to heating.

By forming a highly reflective portion on the amorphous semiconductor layer, the reflectance of which is relatively higher than that of the amorphous semiconductor, and uniformly irradiating the entire surface with laser light, the highly reflective portion The part that has not been formed can be selectively crystallized. The portion where the high-reflecting portion is formed reflects almost no laser light and therefore receives no heat, and only the portion without the high-reflecting portion absorbs the laser light and is heated. By using this method, it is possible to anneal a minute portion such as heating only the semiconductor of the thin film transistor on the semiconductor device.

[0017]

Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) FIG. 1 is a sectional structural view of a semiconductor device having a light receiving element and a TFT according to a first embodiment of the present invention. As shown in FIG. 1, a light receiving element 1 and a switching thin film transistor (hereinafter referred to as TFT) 2 are formed on a glass substrate 10. As a film structure, Al of about 120 nm in thickness is formed on the glass substrate 10.
A film 9 is formed, and a low hydrogenated SiN film 4 having a thickness of about 350 nm is formed on the film 9. Further, in the portion of the light receiving element 1, a non-hydrogenated non-doped amorphous silicon (ia-Si) film 11 having a film thickness of 200 to 300 nm and a TF.
At T2, a polycrystalline silicon (poly-Si) film 5 having a film thickness of 200 to 300 nm and dehydrogenated is formed. The poly-Si film 5 partially has an a-Si film 11. Further thereon, a phosphine-doped amorphous silicon (n + -a-Si) film 6 having a film thickness of 50 nm is formed.
And a Cr / Al two-layer film 7 is formed.

The Al film 9 is formed on the substrate 1 in the light receiving element 1.
It functions as a light-shielding film that shields light incident from the 0 side, and T
In FT2, it functions as a gate electrode. The SiN film 4 functions as a gate insulating film for the light receiving element 1 and the TFT 2. The ia-Si film 11 functions as a photoelectric conversion layer of the light receiving element 1, and the poly-Si film 5 functions as an active layer of the TFT 2. The n + -a-Si film 6 functions as a contact layer of the light receiving element 1, a blocking layer of the TFT 2, and a contact layer. The Cr / Al two-layer film 7 functions as an electrode in the light receiving element 1 and as a source and drain electrode for extracting a photocurrent in the TFT 2. The Al film 9 can also be formed of another metal film such as a Cr film. The SiN film 4 is made of Al
It may be formed of ₂ O ₃ , SiO ₂ , or SiON film. Also,
The Cr / Al two-layer film 7 may be a single layer film of a Cr film or an Al film.

Next, with reference to FIG. 2, an example of the operation when the semiconductor device of this embodiment is used as a contact type image sensor and mounted on a FAX will be described. Light receiving element 1 and T
FT2 (not shown in FIG. 2) is based on the above-mentioned film structure.
The insulating film 200 is further laminated, and the insulating film 200 is further protected by the protective layer 400 and is in close contact with the original 30 fed by the paper feeding mechanism 300. The light emitted from the light emitting element 40, which is a light source, is applied to the document 30, and the reflected light enters the light receiving element 1 of the image sensor and is received. The Al film 9 which is a light-shielding film of the light receiving element 1 prevents light, which is emitted from the light emitting element 40 and has not hit the document 30, from entering from the glass substrate 10 side of the light receiving element 1. The ia-Si film 11 of the photoelectric conversion layer receives the reflected light from the document 30 through the insulating film 200 and generates charges by photoelectric conversion. The generated charge is output as an output signal from the electrode 7 of the light receiving element 1 to the source / drain electrode 7 of the TFT 2 (not shown in FIG. 2) and is switched by the gate electrode 9.

Next, a method of manufacturing the semiconductor device of this embodiment will be described. First, the Al film 9 was formed on the glass substrate 10 by the sputtering method, and patterned by photolithography using wet etching.

Next, the hydrogen-reduced SiN film 4 is subjected to plasma CVD (Chemical Vapor) as follows.
It was formed by the Deposition method. By generating active hydrogen, fluorine or Ar atoms by microwave plasma and exposing the SiN film in the process of forming them,
A SiN film was formed by breaking the weak hydrogen bond of Si-H. Nitrogen was supplied from N radicals to Si whose H was cut off. By using this method, SiN bonds can be easily formed, and the amount of hydrogen in the film is 1 × 10 ²² / cm ³ or less.
An iN film was formed. When monosilane, hydrogen and nitrogen are used as the source gas and the flow rate ratio is set to 1:10:15 and the RF power is set to about 0.1 W / cm ² , the amount of hydrogen in the film is 9 × 10 ²¹ / cm 2. ^A SiN film was formed which was suppressed to a lower value of ³ , had few dangling bonds, and had few defects in the film. On the other hand, as a comparative example, when ammonia gas was used as the source gas, excess hydrogen was taken into the film, and the amount of hydrogen in the film was 3 × 10 ²² / cm ³ , which was not preferable. In addition to the plasma CVD method, a low hydrogenated SiN film 4 could be formed by sputtering a Si ₃ N ₄ target in a hydrogen gas atmosphere using a sputtering method.

A dehydrogenated a-Si film 11 was formed on the dehydrogenated SiN film 4 by a plasma CVD method. This a-Si film 11 is used as it is for the i-
It is used as the a-Si film 11, and a part thereof is polycrystallized by a laser annealing method to be processed into the poly-Si film 5 of the TFT. The low-hydrogenated a-Si film 11 can be processed into the poly-Si film 5 without roughening or peeling of the film surface. When dangling bonds (dangling bonds) increase due to low hydrogenation, a-Si of the light receiving part increases.
Since the photosensitivity of the film 11 is lowered, the proportion of dangling bonds in the film is kept low even if the hydrogen is low. Also,
During the laser annealing, heat is transferred to the lower layer of the a-Si film 11, so that hydrogen is degassed from the lower layer to hydrogenate the upper layer a-Si film 11 to prevent the film surface from being roughened or peeled. As the lower layer, the low hydrogenated SiN film 4 formed by the above method was used.

The a-Si film 11 having a low hydrogen content and a low dangling bond ratio was prepared as follows. First,
A plasma of hydrogen is formed by a microwave of 2.45 GHz, monosilane is supplied as a source gas into the plasma, and the monosilane is decomposed by the microwave plasma to form an a-Si film 1.
1 was formed. Since the above-mentioned hydrogen plasma functions to extract hydrogen, an a-Si film having a hydrogen concentration reduced to 0.5% or more and 9% or less was obtained. Although hydrogen plasma is used here, the same effect can be obtained by using plasma such as argon or fluorine. Also, the decomposition of monosilane is
It could be similarly formed by RF plasma.

On the a-Si film 11, n + -a-Si is formed.
The film 6 was formed by the plasma CVD method. Furthermore, n +-
The light receiving window portion of the light receiving element 1 of the a-Si film 6 and the TFT 2
A window portion between the source and drain of was formed by photolithography and dry etching. Further, the hydrogen-reduced a-Si film and the n + -a-Si film 6 were processed into an island shape by photolithography using dry etching, and were separated into a light receiving element 1 portion and a TFT 2 portion. On top of that, a two-layer film 7 of a Cr / Al film for the source and drain electrodes was laminated by a sputtering method in the order of a Cr film and an Al film. As described above, since the window portion between the source and drain of the TFT 2 was removed in advance, a two-layer film of Cr / Al film was directly laminated on the a-Si film 11. In this way, the step of stacking the Cr film directly on the a-Si film by the sputtering method is used. This is because Cr molecules having high energy collide with the surface of the a-Si film and the Cr film and the a-Si film
This is because a layer of a reaction product of Cr and Si is formed at the interface of the Si film. This reaction product is used as a seed crystal for polycrystallization by laser annealing. The Cr film may be formed by a vapor deposition method or the like other than the sputtering method. In this case, after the formation, a reaction product layer is similarly formed by annealing at 200 ° C. for about 1 hour. You can

Next, the two-layer film 7 of Cr / Al film was patterned by photolithography using wet etching to form a light receiving window portion of the light receiving element 1 and a source / drain electrode of the TFT 2. C of the Al / Cr two-layer film 7
The r film was etched with an aqueous solution of cerium ammonium nitrate. The reaction product of Cr and Si was not removed by wet etching and remained on the a-Si surface.

The portion of the TFT 2 of the a-Si film described above was polycrystallized by heating by the laser annealing method. When the film thickness is relatively thick, the wavelength is as long as 780 nm, and an Ar laser that is incident on the channel region is suitable. Figure 4
As shown in, the reaction product of Cr and Si on the surface of the a-Si film 11 became the seed crystal 41 and was easily polycrystallized at a low heating temperature. Crystals gradually grow from the surface of the a-Si film toward the SiN film 4, and at the interface between the poly-Si film 5 and the gate insulating film 4 where a channel is formed, the crystal grain size is large. It became crystalline silicon and a TFT with high mobility could be formed.

FIG. 5 shows energy states at the time of nucleation in a general crystal nucleation to growth process. As shown in FIG. 5, when there is no seed crystal in advance, the critical nucleus radius r
_If nuclei of ₁ are not formed, crystal growth does not proceed, the free energy for crystal nucleation becomes high, and it becomes necessary to raise the temperature to a high temperature. Due to this high temperature, the poly-Si film 5 becomes
It is easy to cause damage. On the other hand, if the seed crystal 41 as described above is formed in advance, the critical nucleus radius can be reduced to r ₂ , and therefore, nuclei can be generated and polycrystallized at a lower temperature.

Since the distance between the light receiving element 1 and the TFT 2 is narrow, the laser annealing requires accurate selectivity in order to heat only the a-Si film 11 of the TFT 2. Further, in order to improve the manufacturing efficiency, the laser irradiation time is
It is better to have a short time. In the present embodiment, the step of performing laser annealing after forming the electrode 7 allows the electrode layer 7 to act as a metal mask, selectively selecting only the a-Si film portion between the source and drain of the TFT 2.
It was possible to heat using a relatively strong laser output in a short time without damaging other parts. Figure 3
As shown in, when the reflectance (R ₁ ) of the metal mask is higher than the reflectance (R ₂ ) of the a-Si film by 30% or more, the portion covered with the metal mask is generally damaged. However, only the a-Si film is heated. Measurement of the reflectance R _1, R _2, reflectivity R ₂ of the a-Si film is about 60%, the reflectance of the Al film which is the upper electrode layer 7 R
₁ was 90% or more, and was suitable as a metal mask.
If the source / drain electrode 7 cannot be used as a mask in terms of shape, this electrode may be first processed as a mask, irradiated with a laser, and then processed again into the electrode shape.

In this embodiment, the light receiving element 1 having the ia-Si film 11 and the TFT 2 having the poly-Si film 5 are used.
It was possible to fabricate simultaneously with one film structure, and it was possible to reduce the manufacturing process. After forming the low hydrogenated SiN film 4 and the a-Si film, TF is performed by a laser annealing method.
By using the step of heating only the a-Si film of T2 to form the poly-Si film 5, it was possible to manufacture a high-performance TFT 2 without causing surface roughness and film peeling. Also, the low hydrogenated a-S produced by the above-mentioned method
Since the dangling bond of the i film 11 was about the same as when it was produced by the usual method, the performance of the light receiving element 1 was not deteriorated. Further, before laser annealing, Cr and Si reaction products, which will be the seed crystal 41, are formed at the interface between the a-Si film of the TFT 2 and the electrode 7.
Polycrystallization could be easily performed. Since the seed crystal 41 is formed on the surface of the a-Si film, crystallization progresses from the surface portion of the a-Si film 5 toward the interface with the gate insulating film 4 to form a channel insulating film. In the vicinity of the interface with No. 4, polycrystalline silicon having a large crystal grain size was formed, and the TFT 2 having high mobility could be formed.

Poly-Si film 5, ia-Si film 11
Is formed by first forming a hydrogen-free a-Si film by a sputtering method or a thermal CVD method, and then forming a poly-S film.
It is also possible to use a method of heating only a portion of the i film 5 to polycrystallize it, and then hydrogenating the whole with active hydrogen. The patterning of the a-Si film 11 and the n + -a-Si film 6 can also be performed by wet etching. In addition, the Al film 9 and the two-layer film 7 of Cr / Al film
Can also be patterned by dry etching.

When a dry process such as dry etching or ion milling is used for the source / drain etching of the Cr / Al two-layer film 7, the surface of the a-Si film is over-etched to obtain various active species. Strains and defects are generated in the material by hitting with ions or ions, and these strains and defects are used as crystal nuclei instead of the seed crystal 41,
Polycrystallization can be performed. In this case, Cr and Si
Since it is not necessary to form a reaction product, n + -a-Si
The step of etching the window portion between the source and the drain of the film 6 is omitted, and the Cr / Al two-layer film 7 is formed.
The two-layer film 7 and the n + -a-Si film 6 can be continuously dry-etched, and the manufacturing efficiency can be further improved.

As reaction products that can be used as the seed crystal 41, in addition to reaction products of Cr and Si, platinum silicide, which is a reaction product of platinum and Si, and palladium silicide, which is a reaction product of palladium and Si. Etc. For example, when an aluminum alloy is used for the source and drain electrodes 7, silicon or palladium can be used as an alloy additive. This Al-Si
By annealing the -Pd alloy at 200 to 300 ° C, a fine palladium compound is uniformly precipitated in aluminum. Even after the source and the drain are removed by etching, the reaction product deposited at the interface with the active layer remains. When an Al-Si-Pd alloy is used as an electrode, the polycrystallization temperature by laser annealing can be lowered by about 200 ° C, and good polysilicon can be obtained at a low temperature. In addition, A that does not contain silicon as an alloy additive
The l-Pd alloy also has a similar effect by partially absorbing silicon in the active layer. When an Al-1.0% Pd alloy is used, it may be formed by a sputtering method and wet-etched with a mixed acid of phosphoric acid, acetic acid and nitric acid.

The step of performing laser annealing is
It is also possible to perform immediately after the formation of the -a-Si film 11.
In this case, in order to generate the seed crystal 41, the metal film may be once formed by the above-described method and then removed by etching, or the ia-Si film 11 may be removed by ion milling or dry etching. Strains and defects may be generated by hitting by etching.

FIG. 6 shows an example in which the film thickness of the poly-Si film of the TFT 2 is reduced in the same parallel type semiconductor device as in FIG. Other film configurations and manufacturing methods are the same as those described above, except that the a-Si film having a film thickness of 300 nm formed on the light receiving element 1 and the TFT 2 is formed only on the TFT 2 portion.
The film was selectively etched to a film thickness of 100 nm. By thus thinning the poly-Si film 5 of the TFT 2, the off current of the poly-Si film TFT 2 could be further reduced.

(Second Embodiment) A semiconductor device having a light receiving element and a TFT according to a second embodiment of the present invention will be described. The film structure and the function of the film are the same as in Example 1, but the reaction product layer 20 of Cr—Si was used as the blocking layer and the contact layer 6 in FIG. Cr-Si reaction product film 2
Since 0 has a conductivity equal to or higher than that of the n + -a-Si film 6, it can be used as a blocking layer and a contact layer.

A method of manufacturing a semiconductor device according to this embodiment will be described. An Al film 9, a low hydrogenated SiN film 4 and a low hydrogenated a-Si film were formed. The forming method is the same as that of the first embodiment, and therefore its description is omitted. A low hydrogenated a-Si film,
By photolithography using dry etching,
It was processed into an island shape, and the light receiving element 1 portion and the TFT 2 portion were separated. Next, a Cr / Al two-layer film for the source / drain electrodes was formed by sputtering in the order of the Cr film and the Al film. By annealing this at 230 ℃ for 1 hour,
A Cr and Si reaction product layer was formed at the interface between the Cr film and the a-Si film. The reaction product layer of Cr and Si according to the present embodiment is more than that of the reaction product layer according to Example 1 in which annealing is not performed.
Formed thick. Next, a window portion between the source and drain electrodes was formed by photolithography using wet etching. The reaction product layer 20 of Cr and Si was not removed by wet etching and remained on the surface of the a-Si layer. The window portion between the source and drain of the TFT 2 was irradiated with Ar laser, and the reaction product of Cr and Si was used as a seed crystal to polycrystallize the a-Si film to form the poly-Si film 5. After that, the element was completed by removing the reactive biological layer 6 of Cr and Si between the source and drain electrodes by a dry etching method.

The above-mentioned two-layered Cr / Al film 7 is formed at 230 ° C.
Laser annealing may be performed instead of the step of annealing for 1 hour. The power of about a little less than 10% of the laser light reaches the a-Si film through the Cr / Al two-layer film, so that it has the same effect as annealing the Cr / a-Si interface.

In this embodiment, a Cr / Al two-layer film is used as the source / drain electrodes 7, but Al-Pd or Al-Si-Pd may be used. In this case, electrode 7 /
A Pd-Si compound layer is formed on the a-Si interface.

(Embodiment 3) FIG. 7 shows a semiconductor device having a light receiving element and a TFT according to another embodiment of the present invention. As the film structure, the Al film 3 is formed on the glass substrate 10,
On top of that, a SiN film 42 and a film thickness of 10 to 40 nm
Thin poly-Si film 13, thickness 200-500 nm
A-Si film 14 is laminated. On top of that, a phosphine-doped n + -a-Si film 6, Cr
A two-layer film 7 of / Al film is formed.

Al film 9, SiN film 42 and n + -a-
Since the function of the Si film 6 is the same as that of the first embodiment, the description will be omitted. The poly-Si film 13 functions as an active layer of the TFT 2, and the a-Si film 14 functions as a photoelectric conversion layer of the light receiving element 1. The photocurrent generated in the a-Si film 14 of the light receiving element 1 passes through the a-Si film 14 from the source electrode of the TFT 2, flows through the poly-Si film 13, and is again a-Si.
It flows through the membrane 14, flows into the drain electrode 9 and is switched by the gate electrode 9. Pol of the light receiving element
The y-Si film 13 can suppress the dark current to a low level by applying a ground voltage or a negative voltage to the Al film 9 of the light shielding layer. The voltage applied to the Al film 9 of the light shielding layer is usually TF.
Considering that the threshold voltage of T2 is 1 to 3 V, no negative voltage is applied and Al of the light shielding layer of the light receiving element 1 is not applied.
The dark current can be kept low simply by connecting the membrane 9 to ground level.

A method of manufacturing a semiconductor device according to this embodiment will be described. An Al film 9 was formed on the glass substrate 10 by a sputtering method, and patterned by photolithography using wet etching. On top of that, Si
The N film 42 was formed by the usual plasma CVD method. Next, the poly-Si film 13 was formed by the following method. First, a Si film was formed on a substrate by using SiHF-based gas or monosilane and fluorine or hydrogen as a source gas. Next, by exposing this film to active hydrogen or fluorine plasma, hydrogen and fluorine in the film are removed, and fluctuations in the bond distance and bond angle of Si—Si are eliminated to form a poly-Si film 13. .. According to this method, the film can be formed at a low temperature and can be formed without damaging the already formed SiN film 42. Unlike the first embodiment, the poly-Si film 13 does not need to be selectively formed. Therefore, the poly-Si film 13 is formed on the entire surface of the substrate from the time of film formation, and then the a-Si layer is continuously formed. To do. Although the number of steps increases, once the thin a-Si film is formed, the entire surface of the substrate is rapidly heated to about 800 to 1000 ° C. by a method such as laser annealing or rapid thermal annealing (RTA) to crystallize. You may make it.

On top of this, an a-Si film 14 and n + -a-S are formed.
The i film 6 is formed by the plasma CVD method, is processed into an island shape by photolithography, and the Si film 1 of the light receiving element 1 and the TFT 2 is formed.
3, 14, 6 were separated. A two-layer film 7 of Cr / Al is formed thereon by a sputtering method, and photolithography is used to form Cr / Al in the window portion between the light receiving window and the source / drain
The device was completed by removing the Al two-layer film and the n + -a-Si film 6.

In the photoconductor type light receiving element 1 having the structure shown in FIG. 7, the thicker the film thickness, the higher the photoelectric conversion output. Therefore, it is preferable that the film thickness is relatively large, 200 to 500 nm.

In the contact type image sensor of this embodiment, since the light receiving element 1 and the TFT 2 have basically the same film structure, the number of steps can be greatly reduced as compared with the conventional case. For example, in order to form a high-speed poly-Si TFT and an a-Si light receiving element as a conventional contact type image sensor on the same substrate, after forming five coplanar TFTs using a photomask, a light receiving element is formed. It was formed by using three masks. That is, photolithography is performed using a total of eight masks in the process of the conventional contact type image sensor. On the other hand, in the present invention, po
The TFT 2 having the ly-Si film and the light receiving element 1 can be manufactured with only four photomasks. Therefore, the production yield of the high-speed contact image sensor can be more than doubled. In addition, the poly-Si layer and the a-Si
Since the layers can be formed continuously, the semiconductor films for the TFT and the light receiving element can be formed at one time, and the throughput can be significantly improved.

In FIG. 8, the film thickness of the poly-Si film 13 is set to 2
The characteristics of the TFT 2 when the film thickness of the 0-nm, ia-Si film 14 is 300 nm are shown. Active layer is po
Since it is the ly-Si film 13, the mobility μ is 12 cm ² /
A value higher than Vs by one digit or more than that of a normal a-Si TFT was obtained. Further, when the upper portion of the TFT 2 is covered with an insulating film, the off current can be further reduced by about 2 digits.

In FIG. 9, the film thickness of the a-Si film 14 is set to 300.
Photocurrent Iph of the light receiving element 1 when formed as nm
And the dark current Id characteristic are shown. As can be seen from FIG. 9, light /
The dark current ratio is about 80. When an insulating film is formed on the light receiving element 1, the leak current on the element surface can be reduced and the light / dark current ratio can be increased by about one digit.

FIG. 10 shows the characteristics of the laminated TFT of this example and the TFT of the comparative example. As a comparative example, the active layer is a
The characteristics of the laminated TFT 2 having the structure shown in FIG. 7 of this example were compared using an a-Si TFT formed of only the -Si film. The average mobility of a large number of devices on the entire surface of the substrate of the present example was 7.0 cm ² / Vs, which was obtained by the conventional a-SiTF.
It can be seen that it is improved by 15 times or more as compared with T of 0.3 to 0.4 cm ² / Vs. On the other hand, the threshold voltage and the off current are almost the same as those of the a-Si TFT. As shown in FIG. 7, this data is the measured value in the state where the insulating film is not provided on the element surface. Therefore, by providing the insulating film on the element surface, the off current can be further suppressed by about three digits. , When used in an actual circuit, there was no problem at all.

As described above, by using the semiconductor device having the structure shown in FIG. 7 shown in the present embodiment, a semiconductor device having both high photoelectric conversion characteristics and high mobility can be made shorter than half of the conventional one. In the manufacturing process, it is possible to obtain a high yield.

FIG. 11 shows the contact layer, the source and the drain after the a-Si film is processed into a narrow island shape in order to further improve the TFT mobility of the semiconductor device of FIG. This is an example of forming electrodes. In this element structure, the source
The current flowing between the drain electrodes 7 is a-Si having high resistance.
The poly-Si film 13 of the active layer is directly passed through without passing through the film 14.
Therefore, the high field effect mobility of the poly-Si film 13 of the active layer can be used as it is. When the field effect mobility of the TFT 2 having this structure was measured, it was 20
cm ² / Vs was obtained.

FIG. 12 shows the characteristics of the light receiving element 1 and the TFT 2 of the semiconductor device having the film structure shown in FIG.
This is an example in which the TFT 2 is made thinner than the a-Si layer of the light receiving element 1 for optimization. In the light receiving element 1, as the thickness of the a-Si film of the photoelectric conversion layer increases,
The dark current ratio can be increased. On the other hand, in TFT2, aS
As the i film 14 is thinner, the resistance of the a-Si film and the poly-Si film combined increases, and the off current can be reduced when the current is off between the source and drain electrodes.
Therefore, as shown in FIG. 12, the a-Si film 14 is first formed thick so as to be suitable for the light receiving element 1, and then the TF film is formed.
Only the a-Si film 14 of T2 was selectively etched to reduce the film thickness. With the structure shown in FIG. 12, the off current of the TFT could be suppressed low while maintaining a high light / dark current ratio in the light receiving element.

In this embodiment, when the n + -a-Si layer is etched, the poly-Si film 13 and the n + -a-Si layer are formed.
When etching conditions are selected so that a sufficient selection ratio between the film 6 and the etching can be obtained, the a-Si film 1 of the TFT 2 is formed.
A semiconductor device having a structure without 4 can be manufactured.

(Embodiment 4) FIG. 13 shows a TFT according to an embodiment of the present invention. As shown in FIG. 13, the active layer includes an a-Si layer 111 having a hydrogen content of about 1% and a normal a-Si layer 112. A-S with hydrogen content kept as low as 1%
The i-film 111 has a small fluctuation in the bond angle or bond distance of the Si—Si bond, and has high mobility for both electrons and holes. However, since the film is formed by repeating the film formation and the etching, the film formation rate is slow. Therefore, as shown in FIG. 13, an a-Si film 111 having a hydrogen content of about 1% and a normal a-Si film 111 are formed.
With the two-layer structure of the Si film 112, an a-Si TFT having high mobility can be formed with high throughput. The TFT shown in FIG. 13 has an electron mobility of 1 to
It is possible to raise it to about 2 cm ² / Vs. When this TFT is used for a contact type image sensor, it is possible to improve the scanning and reading circuit by devising the method.
It is possible to scan high resolution of 00 dpi at high speed.

(Embodiment 5) FIG. 14 shows an example of a semiconductor device having a light receiving element and a TFT in which the light response of the light receiving element 1 is improved. As shown in FIG. 14, a SiN film 141 having a film thickness of 5 to 50 nm is formed under the n + -a-Si film 6,
As the photoelectric conversion layer, the a-Si film 11 having a hydrogen content of 5% or less was used. Other film configurations were the same as those of the semiconductor device shown in FIG. This SiN film 141 has a thickness of 2 in the light receiving element 1.
The injection of the next photocurrent from the electrode is prevented, and the response of the planar light receiving element 1 is improved. In TFT2, S
The iN film 141 serves as a passivation layer that protects the low-hydrogenated poly-Si film 5 when the n + -a-Si film 6 is etched. The SiN film 141 is a plasma C
It was formed by VD.

When the SiN film 141 was not used, the light responsivity of the light receiving element 1 was 5 msec, but the light responsivity of the light receiving element 1 of this example could be increased to 1 msec. Further, in the present embodiment, a with a hydrogen concentration of 5% or less is used.
Since the -Si film 11 is used, it is possible to improve the photoconductivity by about double digits with a high photocurrent, and it is possible to obtain a semiconductor device having a high-speed photoresponse while having a simple reading circuit.

The TFT 2 shown in FIG. 14 is a poly-S.
Although it has an i-film 5, as shown in FIG.
A laminated structure of a Si film and an a-Si film may be used.

By using the contact type image sensor in the semiconductor device of this embodiment, it is possible to read A4 size in 3 sec with a high definition of 16 lines / mm at a reading speed of 1 msec / line. Therefore, when the contact-type image sensor of this embodiment is used in a facsimile, it is possible to realize a small facsimile with high speed and high definition.

(Embodiment 6) A case where the contact type image sensor to which the present invention is applied is applied to an image sensor portion of a color readable scanner or facsimile will be described.

A color original can be read at a high speed by reading one original at the same time with three sensors using yellow, cyan, and magenta filters, respectively.
At this time, since the width of one sensor can be suppressed within 3 mm by incorporating the scanning circuit constituted by the high-speed poly-Si TFT of the above-mentioned embodiment on the substrate, even three sensors should be thinned to 10 mm or less. Is possible. Furthermore, the number of photomasks used in the manufacturing process is the same as that of the third embodiment.
As described above, since the number is as small as four, even if the number of elements is increased to three, the production yield does not decrease, and the production efficiency can be significantly improved.

[0060]

According to the present invention, a light receiving element having an amorphous semiconductor layer in a photoelectric conversion layer and a thin film transistor having a polycrystalline semiconductor layer in an active layer can be formed on the same substrate with the same film structure. An apparatus and a manufacturing method thereof can be provided. Therefore, it is possible to manufacture a semiconductor device having a highly sensitive light receiving element and a thin film transistor capable of high-speed scanning at a high manufacturing rate.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a semiconductor device of the present invention described in Embodiment 1.

FIG. 2 is a cross-sectional view of a reading unit of a document reading apparatus using the semiconductor device of Example 1 as a contact type image sensor.

FIG. 3 is an explanatory diagram showing reflection of laser light during laser annealing.

FIG. 4 is an explanatory view showing polycrystallization of an a-Si film by laser annealing.

FIG. 5 is a graph showing free energy of a semiconductor during heating.

FIG. 6 is a sectional view of another example of the semiconductor device of the present invention described in the first embodiment.

FIG. 7 is a cross-sectional view of the semiconductor device of the present invention described in Embodiment 3.

8 is a TF of the semiconductor device of the present invention described in Example 3. FIG.
The graph which shows the characteristic of T section.

FIG. 9 is a graph showing the characteristics of the light receiving element portion of the semiconductor device of the present invention described in Example 3;

FIG. 10 shows the T of the semiconductor device of the present invention described in Example 3.
Explanatory drawing which shows the characteristic of FT section.

FIG. 11 is a sectional view of another example of the semiconductor device of the present invention described in the third embodiment.

FIG. 12 is a sectional view of another example of the semiconductor device of the present invention described in the third embodiment.

FIG. 13 is a cross-sectional view of the semiconductor device of the present invention described in Embodiment 4.

FIG. 14 is a cross-sectional view of the semiconductor device of the present invention described in Embodiment 5.

[Explanation of symbols]

1 ... Light receiving element, 2 ... TFT element, 4 ... Low hydrogenated SiN
Membrane, 5 ... Low-hydrogenated poly-Si film, 6 ... n + -a-S
i film, 7 ... Cr / Al two-layer film, 9 ... Al film, 10 ... Glass substrate, 11 ... Low hydrogenated a-Si film, 13 ... poly
-Si film, 14 ... a-Si film, 30 ... Original, 40 ... Light emitting element, 41 ... Seed crystal, 42 ... SiN film, 111 ... Low hydrogenated a-Si film, 112 ... Highly hydrogenated a-Si film, 141 ...
SiN film, 200 ... Insulating film, 400 ... Protective layer.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Internal reference number FI technical display location 9056-4M 311 S (72) Inventor Yoshio Abe 4026 Kuji Town, Hitachi City, Ibaraki Nitate Manufacturing Co., Ltd. Inside Hitachi Research Laboratory (72) Kenichi Hashimoto 4026 Kuji Town, Hitachi City, Hitachi City, Ibaraki Prefecture Hitachi Research Laboratory, Inc. (72) Inventor Yuzo Kozono 4026 Kuji Town, Hitachi City, Ibaraki Prefecture Hitachi Research Laboratory, Ltd. ( 72) Inventor Kazuhiro Ogawa 4026 Kuji Town, Hitachi City, Ibaraki Prefecture Hitachi Research Laboratory, Hitachi Ltd. (72) Inventor Mori Morita 216 Totsuka Town, Totsuka Ward, Yokohama City, Kanagawa Prefecture Hitachi Ltd. Totsuka Factory

Claims (17)

[Claims] 1. A semiconductor device comprising a light receiving element having an amorphous semiconductor layer for photoelectric conversion and a thin film transistor having a polycrystalline semiconductor layer. 2. The semiconductor device according to claim 1, wherein the light receiving element further has a polycrystalline semiconductor layer, and the thin film transistor further has an amorphous semiconductor layer. 3. The semiconductor device according to claim 1, wherein the polycrystalline semiconductor layer of the thin film transistor partially includes an amorphous semiconductor layer. 4. The thin film transistor according to claim 1, wherein the thin film transistor has a source and a drain, and the source and the drain have a reaction product layer of a metal and a semiconductor layer of the thin film transistor. Semiconductor device. 5. The semiconductor device according to claim 1, wherein the polycrystalline semiconductor layer of the thin film transistor has a relatively low hydrogen concentration as compared with other semiconductor layers of the thin film transistor. .. 6. The semiconductor device according to claim 5, wherein the polycrystalline semiconductor layer of the thin film transistor has a lower hydrogenated insulating layer as a lower layer. 7. The semiconductor device according to claim 5, wherein the polycrystalline semiconductor layer is a semiconductor layer having a hydrogen content of 0.5% or more and 9% or less. 8. The semiconductor device according to claim 6 or 7, wherein the insulating film with reduced hydrogen has a hydrogen content of 1 × 10 ²² / cm ³ or less. 9. The polycrystalline semiconductor layer according to claim 1, wherein the polycrystalline semiconductor layer of the thin film transistor has a relatively larger crystal grain size on a side closer to a substrate. Semiconductor device. 10. The semiconductor device according to claim 9, wherein the polycrystalline semiconductor layer of the thin film transistor has a reaction product of a metal and a semiconductor of the thin film transistor on a surface thereof. 11. The semiconductor device according to claim 4, wherein the thin film transistor has an electrode, and the reaction product is a reaction product of a metal forming the electrode and the semiconductor. 12. A thin film transistor having at least one amorphous semiconductor layer, wherein the amorphous semiconductor layer has an amorphous semiconductor layer having a hydrogen concentration of 2% or less. 13. A semiconductor device comprising a substrate, a semiconductor layer for performing photoelectric conversion formed on the substrate, an electrode, and a contact layer for contacting the photoelectric conversion semiconductor layer and the electrode. A semiconductor device comprising an insulating layer provided between a semiconductor layer for photoelectric conversion and the contact layer. 14. A high-reflectance portion having a reflectance relatively higher than that of the amorphous semiconductor is formed on the amorphous semiconductor layer, and the amorphous semiconductor is uniformly irradiated with laser light. By doing so, the semiconductor thin layer in which the high reflection portion is not formed is selectively crystallized, and the method for manufacturing a semiconductor device. 15. A method of manufacturing a semiconductor device, comprising forming a metal film on a semiconductor layer by a sputtering method to form a reaction product layer of the metal and the semiconductor at an interface between the semiconductor and the metal film. .. 16. A reaction product layer of a metal and a semiconductor is formed at an interface between the semiconductor layer and the metal film by forming a metal film on the semiconductor layer and then heat treating the semiconductor layer and the metal film. A method for manufacturing a semiconductor device, which comprises forming the semiconductor device. 17. An image scanner having a light receiving element having a semiconductor layer for reading an original and a thin film transistor having a semiconductor layer for processing an output signal of the light receiving element, wherein the semiconductor layer of the light receiving element is an amorphous semiconductor layer. And a semiconductor layer of the thin film transistor having a polycrystalline semiconductor layer.